The heart of a computer is a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a write/read head assembly that is suspended by a suspension arm adjacent to a surface of the rotating magnetic disk, and an actuator that swings the suspension arm to place the write/read head assembly over selected circular tracks on the rotating magnetic disk. The write/read head assembly is directly located on a slider that has an air bearing surface (ABS) facing the surface of the magnetic disk. When the magnetic disk is stationary, the suspension arm biases the slider into contact with the surface of the magnetic disk. When the magnetic disk rotates, air is swirled by the rotating magnetic disk. When the slider rides on the air bearing, the write/read assembly is employed for writing magnetic impressions to and reading magnetic impressions from the rotating magnetic disk. The write/read head assembly is connected to processing circuitry that operates according to a computer program to implement the write and read functions.
The write/read head assembly includes a write head and a read head. The write head includes first and second write-pole layers, a write-gap layer, a coil layer, and first, second and third insulation layers (an insulation stack). The write-gap layer, coil layer and insulation stack are sandwiched between the first and second write-pole layers. The first and second write-pole layers are connected at the back of the write head. Current conducted to the coil layer induces a magnetic flux in the first and second write-pole layers which cause a magnetic field to fringe out at the ABS of the write head for the purpose of writing the aforementioned magnetic impressions in circular data tracks on the aforementioned rotating magnetic disk.
Referring now to FIG. 1, there is shown a magnetic disk drive 100 embodying this invention. As shown in FIG. 1, at least one rotatable magnetic disk 112 is supported on a spindle 114 and rotated by a disk drive motor 118. The magnetic recording is conducted by writing and reading circular data tracks (not shown) on the rotating magnetic disk 112.
At least one slider 113 is positioned near the magnetic disk 112, each slider 113 supporting one or more write/read head assemblies 121. As the magnetic disk 112 rotates, the slider 113 moves radially in and out over the disk surface 122 so that the write/read head assembly 121 may access different circular data tracks on the disk surface 122. Each slider 113 is attached to an actuator arm 119 with a suspension 115. The suspension 115 provides a slight spring force which biases the slider 113 against the disk surface 122. Each actuator arm 119 is connected with a voice coil motor (VCM) 127. The VCM 127 comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by a control unit 129.
During operation of the magnetic disk drive 100, the rotation of the magnetic disk 112 generates an air bearing between the slider 113 and the disk surface 122, which exerts an upward force or lift on the slider 113. The air bearing thus counter-balances the slight spring force of the suspension 115 and supports the slider 113 off and slightly above the disk surface 122 by a small, substantially constant spacing during normal operation.
The various components of the magnetic disk drive 100 are controlled in operation by control signals generated by the control unit 129, such as access control signals and internal clock signals. Typically, the control unit 129 comprises logic control circuits, storage means and a microprocessor. The control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123, and head position and seek control signals on line 128. The control signals on line 128 provide the desired current profiles to optimally move and position the slider 113 to the desired circular data track on the disk surface 122. Write and read signals are communicated to and from the write/read head assembly 121 with a recording channel 125.
With reference to FIG. 2, the orientation of the write/read head assembly 121 in the slider 113 can be seen in more detail. FIG. 2 is an ABS view of the slider 113, and as can be seen, the write/read head assembly 121, including a write head and a read head, is located at a trailing edge of the slider 113. The above description of a typical magnetic disk drive 100, and the accompanying illustration of FIGS. 1 and 2 are for representation purposes only. It should be apparent that this invention may be embodied in other data storage systems similar to the magnetic disk drive 100. These data storage systems may contain a large number of magnetic disks and actuators, and each actuator may support a number of sliders.
A read head commonly used in a current-in-plane (CIP) mode, as shown in FIG. 3, includes first and second magnetic-shield layers (not shown), first and second read-gap layers 326, 328, a giant magnetoresistance (GMR) sensor 302 in a read region, longitudinal bias layers 330 in two side regions, and conductor layers 332 also in the two side regions. The GMR sensor 302, the longitudinal bias layers 330, and the conductor layers 332 are sandwiched between the first and second read-gap layers 326, 328, which are in turn sandwiched between the first and second magnetic-shield layers (not shown). A commonly used GMR sensor 302 comprises Al—O/Ni—Cr—Fe/Ni—Fe seed layers 322, an antiferromagnetic Pt—Mn transverse pinning layer 316, a synthetic pinned-layer structure 306 (comprising a ferromagnetic Co—Fe first pinned layer 310 with a magnetization 318, a nonmagnetic Ru spacer layer 314, and a ferromagnetic Co—Fe second pinned layer 312 with a magnetization 320), a nonmagnetic conducting Cu—O spacer layer 308, ferromagnetic Co—Fe/Ni—Fe sense layers 304 with a magnetization 336, and a nonmagnetic Ta cap layer 324. In a quiescent position when a sense current is conducted through the GMR sensor 302, the magnetization 318 of the Co—Fe first pinned layer 310 is rigidly pinned in a transverse direction perpendicular to and away from the ABS, the magnetization 320 of the Co—Fe second pinned layer 312 is also rigidly pinned in a direction perpendicular to but toward the ABS, and the magnetization 336 of the Co—Fe/Ni—Fe sense layers 304 is oriented in a longitudinal direction parallel to the ABS. During sensor operation, only the magnetization 336 of the Co—Fe/Ni—Fe sense layers 304 is free to rotate in positive and negative directions from the quiescent position in response to positive and negative magnetic signal fields from the adjacent rotating magnetic disk.
The thickness of the Cu—O spacer layer 308 is chosen to be less than the mean free path of conduction electrons through the GMR sensor 302. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the Cu—O spacer layer 308 with the Co—Fe second pinned layer 312 and with the Co—Fe/Ni—Fe sense layers 304. When the magnetization 320 of the Co—Fe second pinned layer 312 and the magnetization 336 of the Co—Fe/Ni—Fe sense layers 304 are parallel to each other, scattering is minimal. When the magnetizations 320, 336 are antiparallel to each other, scattering is maximal. Changes in scattering alter the resistance of the GMR sensor 302 in proportion to cos θ, where θ is the angle between the magnetizations 320, 336. During sensor operation, the resistance of the GMR sensor 302 changes proportionally to the magnitudes of the magnetic fields from the rotating magnetic disk, and these resistance changes cause potential changes that are detected and processed as playback signals.
In the prior-art fabrication process of the GMR sensor 302 abutted with the longitudinal bias layers 330 and conductor layers 332 in the two side regions, as shown in FIG. 3, the GMR sensor 302 comprising Al—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Pt—Mn(15)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Cu—O(1.8)/Co—Fe(1)/Ni—Fe(1.6)/Ta(4) films (thickness in nm) is deposited in a deposition field of 100 Oe on a 8.2 nm thick Al2O3 first read-gap layer 326. A transverse-field anneal is applied in a field of 50,000 Oe for 5 hours at 265° C. in a direction perpendicular to the deposition field. A monolayer photoresist is applied and patterned in a photolithographic tool to mask the GMR sensor 302 in a read region. Ion milling is then applied to entirely remove the GMR sensor 302 and partially remove the Al2O3 first read-gap layer in two exposed side regions, in order to form sharp contiguous junctions. Longitudinal bias and conductor layers 330, 332, comprising Cr(15)/Co—Pt—Cr(10)/Rh(45) films are then deposited into the two exposed side regions, preferably with ion-beam sputtering at a normal angle for abutting the GMR sensor 302. The monolayer photoresist is lifted off with assistance of chemical mechanical polishing (CMP). After a subsequent similar patterning process, recessed conductor layers comprising Ta(10)/Cu(60)/Ta(10) films (not shown) are deposited. After a monolayer photoresist is lifted off, a 8.2 nm thick Al2O3 second read-gap layer 328 is then deposited.
The GMR sensor 302 requires the transverse-field anneal to develop strong antiferromagnetic/ferromagnetic coupling between the Pt—Mn transverse pinning layer 316 and Co—Fe first pinned layer 310. The anneal field must exceed the saturation field (HS) of antiparallel (AP) ferromagnetic/ferromagnetic coupling across the Ru spacer layer 314 (˜8,000 Oe) for aligning the magnetization 318 of the Co—Fe first pinned layer 310 and the magnetization 320 of the Co—Fe second pinned layer 312 in the transverse direction. After cooling to room temperature, the magnetization 318 is rigidly pinned by the Pt—Mn transverse pinning layer 316 in the transverse direction, while the magnetization 320 is rotated by 180°. A transverse flux closure will be formed between the magnetizations 318 and 320 after patterning, resulting in a small net magnetization in the Co—Fe/Ru/Co—Fe synthetic pinned-layer structure 306. This small net magnetization induces a small demagnetizing field (HD) in the Co—Fe/Ni—Fe sense layers 304.
In this GMR sensor 302, antiferromagnetic/ferromagnetic coupling occurs between the Pt—Mn transverse pinning layer 316 and the Co—Fe/Ru/Co—Fe pinned-layer structure 306, producing a pinning field (HP). This HP must be high enough to rigidly pin the magnetizations 318 and 320 of the Co—Fe/Ru/Co—Fe pinned layer structure 306 for proper sensor operation. Ferromagnetic/ferromagnetic coupling also occurs across the Cu—O spacer layer 308, producing a negative ferromagnetic coupling field (HF). This HF must be precisely controlled so that the sum of HF and HD counterbalances a current-induced field (HI) in the Co—Fe/Ni—Fe sense layers 304 (HF+HD=HI), thereby orienting the magnetization 336 of the Co—Fe/Ni—Fe sense layers 304 in a longitudinal direction parallel to the ABS for optimally biased sensor operation. In a quiescent position, this GMR sensor 302 exhibits a resistance of Ro+RA+(½)RG, where Ro is a nonmagnetic resistance, RA is the maximum anisotropy magnetoresistance (AMR) of the Co—Fe/Ni—Fe sense layers 304, and RG is the maximum giant magnetoresistance (GMR) resistance. When receiving a signal field from a rotating magnetic disk, the magnetization 336 rotates from the longitudinal direction, while the magnetizations 318, 320 remain unchanged. The rotation of the magnetization 336 changes the resistance of the GMR sensor 302 by ±ΔRG sin θ1−ΔRA sin2 θ1, where θ1 is a rotation angle.
There are several disadvantages in the use of the GMR sensor with this hard magnetic stabilization scheme, as described in the prior art. First, to attain stable GMR responses, the Cr film in the side regions must be deposited thick enough to align die midplane of the Co—Pt—Cr hard magnetic layer with that of the Co—Fe/Ni—Fe sense layers of the GMR sensor, and thus the Cr film at the contiguous junctions is inevitably thick. As a result, the separation between the sense layers and the Co—Pt—Cr hard magnetic layer becomes large, and the stabilization efficiency is substantially reduced. Second, the Rh conductor layer must be thick enough to provide a low-resistance path, and thus substantial overhangs at sides of the monolayer photoresist are formed. As a result, the liftoff process becomes difficult, and the sensor width cannot be precisely determined. Third, the CMP is typically applied to facilitate the liftoff process, and thus possible damages to the Co—Fe/Ni—Fe sense layers remain a concern. Fourth, in this hard magnetic stabilization scheme, longitudinal bias fields provided by the Co—Pt—Cr hard magnetic layer are very non-uniform, which are high at edges of the sense layers, causing difficulties in rotating the magnetization of the sense layers, and are low at the center of the sense layers, causing difficulties in stabilizing, the sense layers.
On the other hand, a read head 400 recently used in a current-perpendicular-to-plane (CPP) mode, as shown in FIG. 4, includes first and second magnetic-shield layers 426, 428, a tunneling magnetoresistance (TMR) sensor 402 (or a GMR sensor 402), a longitudinal bias (LB) stack 440, and insulating layers 430. The TMR sensor 402 is connected with the first magnetic-shield layer 426 and overlaid with the LB stack 440, which is connected with the second magnetic-shield layer 428.
The TMR sensor 402 comprises a Ta seed layer 422, an antiferromagnetic Pt—Mn transverse pinning layer 416, a synthetic pinned layer structure 406 (comprising a ferromagnetic Co—Fe first pinned layer 410 having a magnetization 418, a nonmagnetic Ru spacer layer 414, and a ferromagnetic Co—Fe second pinned layer 412 having a magnetization 420), a nonmagnetic insulating Al—O barrier layer 408, ferromagnetic Co—Fe/Ni—Fe sense layers 404 having a magnetization 436, and a nonmagnetic Cu cap layer 424. A recently used LB stack 440 comprises a nonmagnetic Ru seed layer 442, a ferromagnetic Co—Fe longitudinal pinned layer 444 having a magnetization 438, an antiferromagnetic Ir—Mn longitudinal pinning layer 446, and a nonmagnetic Ta cap layer 448.
In the prior-art fabrication process of a TMR sensor 402 overlaid with an LB stack 440 in a read region and abutted with insulating layers in two side regions, as shown in FIG. 4, the TMR sensor 402 comprising Ta(6)/Pt—Mn(15)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.8)/Al—O(0.8)/Co—Fe(1)/Ni—Fe(1.6)/Cu(2) films is deposited in a deposition field of 100 Oe on a 1 μm thick Ni—Fe first magnetic-shield layer 426. The LB stack 440 comprising Ru(1)/Co—Fe(2.8)/Ir—Mn(7.5)/Ta(10) films is then subsequently deposited in the same deposition field on the TMR sensor. A transverse-field anneal is applied in a field of 50,000 Oe for 5 hours at 265° C. in a direction perpendicular to the deposition field. A longitudinal-field anneal is then applied in a field of 200 Oe for 2 hours at 240° C. in a directional antiparallel to the deposition field. A monolayer photoresist is applied and patterned in a photolithographic tool to mask the TMR sensor 402 and the LB stack 440 in a read region. Ion milling is then applied to entirely remove the LB stack 440 and the TMR sensor 402, and partially remove the Ni—Fe first magnetic-shield layer 426 in two exposed side regions. A 50 nm thick Al2O3 insulating layer 430 is then deposited into the two exposed side regions. The monolayer photoresist is lifted off, with assistance of CMP, and a 1 μm thick Ni—Fe second magnetic-shield layer 428 is then deposited.
The TMR sensor 402 requires the transverse-field anneal to develop strong antiferromagnetic/ferromagnetic coupling between the Pt—Mn transverse pinning layer 416 and the Co—Fe first pinned layer 410. The anneal field must exceed the saturation field (HS) of AP ferromagnetic/ferromagnetic coupling across the Ru spacer layer 414 (˜8,000 Oe) for aligning the magnetization 418 of the Co—Fe first pinned layer 410 and the magnetization 420 of the Co—Fe second pinned layer 412. After cooling to room temperature, the magnetization 418 is rigidly pinned by the Pt—Mn transverse pinning layer 416 in the transverse direction, while the magnetization 420 is rotated by 180°. A transverse flux closure will be formed between the magnetizations 418 and 420 after patterning, resulting in a small net magnetization in the Co—Fe/Ru/Co—Fe synthetic pinned-layer structure 406. This small net magnetization induces a small demagnetizing field (HD) in the Co—Fe/Ni—Fe sense layers 404.
The LB stack 440 requires the longitudinal-field anneal to establish strong ferromagnetic/anti ferromagnetic coupling between the Co—Fe longitudinal pinned layer 444 and the Ir—Mn longitudinal pinning layer 446. The anneal field only needs to exceed the unidirectional anisotropy field (HUA) of the as-deposited Co—Fe longitudinal pinned and Ir—Mn longitudinal pinning layers 444, 446 (about 100 Oe) at 240° C. for aligning the magnetization 438 of the Co—Fe longitudinal pinned layer 444 in a directional antiparallel to the deposition field. After cooling to room temperature, the magnetization 438 of the Co—Fe longitudinal pinned layer 444 is rigidly pinned by the Ir—Mn longitudinal pinning layer 446. As a result, a longitudinal flux closure will be formed between the magnetization 438 of the Co—Fe longitudinal pinned layer 444 and the magnetization 436 of the Co—Fe/Ni—Fe sense layers 404 after patterning, inducing magnetostatic interaction needed for stabilizing the Co—Fe/Ni—Fe sense layers 404. Since this anneal field is much lower than the spin-flop field (HSF) of AP coupling across the Ru spacer layer 444 (˜1,000 Oe), the transverse flux closure between the magnetization 418 of the Co—Fe first pinned layer 410 and the magnetization 420 of the Co—Fe second pinned layer 412 is not interrupted.
In this TMR sensor 402, antiferromagnetic/ferromagnetic coupling occurs between the Pt—Mn transverse pinning layer 416 and the Co—Fe/Ru/Co—Fe synthetic pinned layer structure 406, producing a transverse pinning field (HP). This Hp must be high enough to rigidly pin the magnetizations 418 and 420 of the Co—Fe/Ru/Co—Fe synthetic pinned layer structure 406 for proper sensor operation. Ferromagnetic/ferromagnetic coupling also occurs across the Al—O spacer layer, producing a positive ferromagnetic coupling field (HF). This HF must be precisely controlled to counterbalance HD in the Co—Fe/Ni—Fe sense layers 404 (HF=HD), thereby orienting the magnetization 436 of the Co—Fe/Ni—Fe sense layers 404 in a longitudinal direction parallel to the ABS for optimally biased sensor operation. In a quiescent position, this TMR sensor 402 exhibits a resistance of Ro+(½)ΔRT, where Ro is a nonmagnetic resistance, ΔRT is the maximum tunneling magnetoresistance (TMR) resistance. When receiving a signal field from a rotating magnetic disk, the magnetization 436 rotates from the longitudinal direction, while the magnetizations 418, 420 and 438 remain unchanged. The rotation of the magnetization 436 changes the resistance of the TMR sensor 402 by ±ΔRT sin θ1, where θ1 is a rotation angle.
There are several disadvantages in the use of the TMR sensor with the antiferromagnetic stabilization scheme, as described in the prior art. First, the Pt—Mn transverse and Ir—Mn longitudinal pinning layers require the transverse-field and longitudinal-field anneals, respectively. While it is feasible to achieve the coexistence of the transverse and longitudinal flux closures with this dual-anneal approach, it appears difficult in attaining a very high HUA needed for the longitudinal flux closure due to the inherent weaker antiferromagnetism in the Ir—Mn longitudinal pinning layer than the Pt—Mn transverse pinning layer. Second, it is challenging to precisely control the total thickness of nonmagnetic Cu and Ru films used as decoupling layers. The Cu decoupling layer is needed to control the magnetostriction of the underlying sense layers, while the Ru decoupling layer is needed to facilitate the LB stack to attain a high HUA. Their total thickness should be optimized in order to diminish ferromagnetic/ferromagnetic coupling between the sense and longitudinal pinned layers, while still ensuring strong magnetostatic interactions between the sense and longitudinal pinned layers. Third, in this antiferromagnetic stabilization scheme, longitudinal bias fields provided by the LB stack are very non-uniform, which are high at edges of the sense layers, causing difficulties in rotating the magnetization of the sense layers, and are low at the center of the sense layers, causing difficulties in stabilizing the sense layers.
In order to meet the ever increasing demand for improved data rate and data capacity, researchers have found ways to make the read sensor ever smaller. For instance, by reducing the sensor width, researchers have been able to fit ever more tracks of data onto a given area of a magnetic disk. However, as the sensor widths decrease, the traditional hard stabilization scheme for the GMR sensor used in the CIP mode, and the antiferromagnetic stabilization scheme for either the GMR or TMR sensor used in the CPP mode, as described previously, become insufficient to stabilize the sense layers. As discussed above, in the traditional hard stabilization and antiferromagnetic stabilization schemes, longitudinal bias layers magnetostatically couple to the outer side edges of the sense layers, providing strong longitudinal bias fields at edges of the read sensor. However, these longitudinal bias fields decay significantly toward the center of the read sensor. As the read sensor is made narrower, the demagnetizing field within the read sensor substantially increases, thus causing more difficulties in stabilizing the sense layers. Hence, a novel stabilization scheme is needed very much for the ever narrowed read sensor.